applicability of 802.1qbu and 802.1qbv to fronthaul...applicability of 802.1qbu and 802.1qbv to...
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Applicability of Qbu and Qbv to Fronthaul
János Farkas and Balázs Varga [email protected] [email protected]
November 11, 2015
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 2
› Common Public Radio Interface (CPRI) traffic vs background (BG) traffic
– IEEE 802.1Qbu - Frame Preemption (with IEEE 802.3br IET) – IEEE 802.1Qbv - Enhancements for Scheduled Traffic – 802.1Qbu and 802.1Qbv with guard band
› Concurring CPRI flows
Outline
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 3
› Tree topology comprised of 10 Gbps links › Switching delay: 1500 ns ± 5 ns variation › CPRI traffic
– Rate: 1.228 Gbps – Payload: 300 bytes – Period: 1954 ns
› Background traffic – CBR
› Payload: 1500 bytes › Period: 9770 ns
– VBR › Payload: rnd 1000-1500 bytes › Period: 5000 ns ± 500 ns
Evaluated Use Case
uplink Radio Equipment (RE) Radio Equipment Controller (REC)
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
BGD src
BGD dst
B2
BG
A1
B1
A2
RE-B2
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 4
› The effects of background traffic on CPRI are investigated first
› There is no race condition between CPRI flows in these cases
– The simulation set-up is designed to avoid CPRI race conditions – Frames of CPRI flows always arrive at the switches in the same
order and they are always served by the switches in the same order
› Packet Delay Variation (PDV) is determined as the difference between the largest and the smallest delay that frames of a given flow suffer
CPRI vs Background Traffic
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 5
4. Preemption is not possible if frame < 124 bytes
– Max Delay = 114.4ns
3. Preemption req. too late – Max Delay = 60.8ns
2. Preemption req. at the beginning – transmission of BG frame just started – Preemption Delay = 67.2ns
1. Preemption req. in the middle – Preemption Delay = 13.6ns – FCS + IFG + remaining bits of current octet
Frame Preemption Event Possibilities
frame flow direction
› 64-byte fragment size is used in all cases (10 Gbps link)
pre includes Preamble and Start mPacket delimiter (SMD)
BG
original BG frame
Preemption request
IFG
IFG
BG
remainingfragment
of BG frame
pre MCRC preFCS header
express
express
BG
BG frame
Preemption request
IFGFCS preheader
< 64BBG
express
BG frame < 124B
IFGFCS preheader
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 6
Frame Preemption Results
Flow Min delay [ns] Max delay [ns] PDV [ns] B2 13832.4 13832.4 0 A2 19693.2 19760.4 67.2 A1 26154.0 26227.5 73.5 B1 26754.0 26827.5 73.5
Flow Min delay [ns] Max delay [ns] PDV [ns] B2 13532.4 13532.4 0 A2 19693.2 19760.4 67.2 A1 25854.0 25953.5 99.5 B1 26154.0 26265.1 111.1
no variation in switching delay
BG
B2
A2
B1 A1
Preemption on Preemption off
B2
A2
B1 BG
A1
Preemption on Preemption off
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
BGDsrc
BGDdst
B2
BG
A1
B1
A2
RE-B2
SW
2
260.8ns
1 ‚cycle’ = 1954ns
600ns
1200ns
260.8ns
260.8ns
A1, B1:
A2:
SW
2
1 ‚cycle’ = 1954ns
600ns 260.8ns
A1, B1:
A2:
260.8ns
300ns
260.8ns
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 7
Enhancements for Scheduled Traffic
B2
A2
B1
BG
A1
Flow Min delay [ns] Max delay [ns] PDV [ns] B2 12812 12842 29.9 A2 19680 19719 39.5 A1 25840 25888 47.9 B1 26150 26198 47.9 BG 28484.0 30453.1 1970.3
Traffic source synchronization inaccuracy: ± 10 ns
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
BGDsrc
BGDdst
B2
BG
A1
B1
A2
RE-B2
Gate on 900-byte background at SW3:
SW
3
Gate on 900-byte background at SW2:
SW
2
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 8
› No variation in switching delay › VBR background › 50ns guard band: max PDV = 17.2ns › 70ns guard band: PDV = 0 (no PDV due to BG traffic)
Frame Preemption and Enhancements for Scheduled Traffic with Guard Band
Flow Min delay [ns] Max delay [ns] PDV [ns] B2 13832.4 13832.4 0 A2 19702.4 19719.6 17.2 A1 26164.4 26181.6 17.2 B1 26764.4 26781.6 17.2
50 ns guard band
300ns
A1, B1:
1 ‚cycle’ = 1954ns
A2: 600ns
260.8ns
BG: HOLD RELEASE
Guard Band
Open Express Gate:
Closed Open Open Closed Closed
transmit RELEASE
SW
2
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
BGDsrc
BGDdst
B2
BG
A1
B1
A2
RE-B2
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 9
Frame Preemption and Enhancements for Scheduled Traffic with Guard Band
› No variation in switching delay › VBR background › 50ns guard band: max PDV = 17.2ns › 70ns guard band: PDV = 0 (no PDV due to BG traffic)
Flow Min delay [ns] Max delay [ns] PDV [ns] B2 13532.4 13532.4 0 A2 19702.4 19719.6 17.2 A1 25863.2 25880.4 17.2 B1 26154.0 25154.0 0
50 ns guard band
SW
2
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
BGDsrc
BGDdst
B2
BG
A1
B1
A2
RE-B2
300ns
A1, B1:
1 ‚cycle’ = 1954ns
A2: 600ns
260.8ns
260.8ns
transmit BG: RELEASE
Guard Band
Open Express Gate:
Closed
HOLD
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 10
Concurrent Express Frames
reference tA-arrive
PDVA
tB-arrive
observed frame B
frame A
frame B is sent first (no impact on frame B)
frame B is sent second (flow B is
influenced by PDV of flow A)
frame order may change
(largest impact
on frame-B)
frame flow direction
frame B is sent second (no impact on frame B)
Effect of frame A on frame B depending on the relative arrival of frame B to frame A
frame B is sent second
(flow B inherits PDV of flow A)
PDVA tA-earliest-arrive tA-latest-arrive
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 11
› Racing shuffles order › This causes PDV
CPRI flows May Race at Each Hop
SW-3
SW-2
SW-1
REC-A
REC-B
RE-A1
RE-B1
RE-A2
B2
B1
A1
A2
RE-B2
Traffic source synchronization inaccuracy: ± 10 ns
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 12
SW-3
Delaying at Ingress to the Network
Indeterminate order: PDV = 280ns Deterministic order: PDV = 0ns
SW-3
SW-2
SW-1
REC-A
REC-B
Delay-1
D
Delay-2
D
A1
B1
RE-A1
RE-B1
Traffic source synchronization inaccuracy: ± 10 ns
SW-3
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 13
› 802.1Qbu – Frame Preemption (with 802.3br) – It is essential for being able to cope with large background frames – Its worst-case PDV can be calculated
› 802.1Qbv – Enhancements for Scheduled Traffic – It can be used to cope with background traffic
› 802.1Qbu and 802.1Qbv with guard band – Zero PDV can be achieved
› Concurrent CPRI flows
– Indeterminate order can cause significant PDV – This effect can be avoided by assuring deterministic order, e.g.,
by intentional delaying
Summary
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 14
› The authors thank Csaba Simon, Maliosz Markosz, József Bíró, Miklós Máté, Árpád Nagy, and István Moldován for their contributions.
Acknowledgements
Applicability of 802.1Qbu and 802.1Qbv to fronthaul | 2015-11-11 | Page 15